1. Field of the Invention
The present invention generally relates to pattern inspection methods, and pattern inspection apparatuses, and recording media which store pattern inspection programs. More particularly, the present invention relates to a pattern inspection method and a pattern inspection apparatus for pattern inspection by the use of an electro-optical system, and a recording medium which records a pattern inspection program.
As pattern designs on printed wiring boards or photomasks have been rapidly improved by programs such as a CAD (Computer Aided Design) program, pattern inspection has been becoming more and more important, because of the increasing difficulties in guaranteeing high quality and high performance. There are two types of pattern inspection methods: one is a continuity inspection type, and the other is a visual inspection type.
As a conventional pattern inspection method of the visual inspection type, there is a die-to-die inspection technique for carrying out pattern inspection by comparing two neighboring chips (dies). Also, there is a die-to-database inspection technique for carrying out pattern inspection by comparing a chip with design data.
2. Description of the Related Art
FIG. 1 is a block diagram of a die-to-die pattern inspection apparatus and a die-to-database pattern inspection apparatus. FIG. 2 is a flowchart of operations of the apparatuses shown in FIG. 1.
The apparatus comprises two optical detectors (objectives) 4a and 4b. The optical detector 4a and a light receiving member 6a capture the image data of a chip 3a (step S16), and the optical detector 4b and a light receiving member 6b capture the image data of a chip 3b to be inspected (step S22). The captured data of the chip 3a is stored in an image memory 7a (step S20), while the captured image data of the chip 3b is stored in an image memory 7b (step S24). Here, the optical detectors 4a and 4b are situated in such positions that they can simultaneously scan the image data at the same locations on the chips 3a and 3b. 
The above process is the image data capturing process in the die-to-die pattern inspection. In the case of the die-to-database pattern inspection, on the other hand, a data conversion unit 14 converts design data 16 into image data (step S30), and the converted data, instead of the image data captured by the optical detector 4a and the light receiving member 6a, is stored in the image memory 7a (step S20).
In both cases of the die-to-die pattern inspection and the die-to-database pattern inspection, a pattern compound circuit 8 compares the image data stored in the image memory 7a with the image data stored in the image memory 7b (step S36), and supplies the comparison result to a defect detecting circuit 9. In accordance with the comparison result, the defect detecting circuit 9 detects defects (step S38).
Although the apparatuses shown in FIG. 1 have the two optical detectors 4a and 4b, it is also possible to employ only one optical detector in the die-to-die pattern inspection. FIG. 3 is a block diagram of another die-to-die pattern inspection apparatus. FIG. 4 is a flowchart of the apparatus of FIG. 3. In these figures, the same components as in FIGS. 1 and 2 are denoted by the same reference numerals.
The apparatus of FIG. 3 has an optical detector (an objective) 4. The optical detector 4 and a light receiving member 6 capture the image data of the chip 3a (step S56). A switch 17 is then connected to the image memory 7a so as to store the image data of the chip 3a in the image memory 7a (step S58). The optical detector 4 and a light receiving member 6 capture the image data of the other chip 3b (step S56). This time, the switch 17 is connected to the image memory 7b so as to store the image data of the chip 3B in the image memory 7b (step S60).
The pattern compound circuit 8 then compares the image data stored in the image memory 7a with the image data stored in the image memory 7b (step S62), and supplies the comparison result to the defect detecting circuit 9. In accordance with the comparison result, the defect detecting circuit 9 detects defects (step S64).
Each of the defects detected as shown in the flowcharts of FIGS. 2 and 4 is checked by visual inspection. FIG. 5 is a flowchart of the defect evaluation procedure.
After the defect detection is completed, the detected defects are read out of a defect information memory 10 one by one (step S84), and the read-out information is processed so that the position of each defect can be visually seen (step S86). For instance, the defective point is enlarged and displayed.
A user evaluates the defects one by one, and determines whether the defect is a false defect that is allowable (step S88). The false defects are not pattern disconnection or short circuits, but are differences between the design data and each chip. For instance, the round corners of patterns formed on a chip represent such differences.
If the defect is determined to be a false defect, the defect information corresponding to the defect is rewritten (step S90). This process is carried out for every detected defect, so that false defects are eliminated from the final defect data set.
In the die-to-die pattern inspection using the apparatus shown in FIG. 1, however, the two optical detectors 4a and 4b complicate the structure, resulting in high production costs. The die-to-die pattern inspection using the apparatus shown in FIG. 3 also has a problem that a large-capacity image memory is required, which also results in high production costs.
In the die-to-database pattern inspection, it is necessary to prepare the design data and convert the design data into image data for inspection. This data conversion takes a very long time and results in poor operation efficiency.
In any of the above inspections, pattern images should be accurately compared, and therefore a high-precision apparatus is required.
Furthermore, patterns formed on a chip normally have round corners, and cannot be compared with the image data converted from the design data. To perform proper comparisons, the round corners need to be adjusted for. However, it is difficult to process adjustments for the round corners, because such a process often leads to wrong detection and many false defects. To avoid the wrong detection, the defect evaluation procedure shown in FIG. 5 is needed in order to evaluate defect information containing false defect information so as to eliminate the false defects from the final defect data set. However, the defect evaluation procedure takes a very long time, and the visual evaluation often reduces inspection reliability.
A general object of the present invention is to provide pattern inspection methods, pattern inspection apparatuses, and recording media which store pattern inspection programs, in which the above disadvantages are eliminated.
A more specific object of the present invention is to provide a pattern inspection method and a pattern inspection apparatus, by which pattern inspection is carried out with a simpler mechanical configuration following a simpler procedure. Another specific object of the present invention is to provide a recording medium which records a pattern inspection program for carrying out pattern inspection by the above pattern inspection method or the above pattern inspection apparatus.
The above objects of the present invention are achieved by a pattern inspection method which comprises the steps of:
generating first image data from a pattern image captured from a sample;
obtaining a first pattern number which is the number of patterns contained in the first image data;
generating second image data by reducing the four sides of each pattern contained in the first image data by a predetermined width;
obtaining a second pattern number which is the number of patterns contained in the second image data; and
detecting a defect in the patterns of the sample in accordance with a result of comparison between the first pattern number and the second pattern number.
According to the above method, a defect contained in the pattern of the sample is detected based on the result of comparison between the number of patterns contained in the first image data and the number of patterns contained in the second image data. This is simpler than a conventional defect detection technique of detecting a defect by comparing the image data of two samples. Accordingly, pattern defect detection can be carried out with a simpler mechanical configuration following a simpler procedure.
Also, the pattern inspection method of the present invention does not include the conventionally required step of eliminating false defects. Thus, operation efficiency can be improved.
The above objects of the present invention are also achieved by a pattern inspection apparatus which comprises: a first image data generator which generates first image data from a pattern image captured from a sample; a second image data generator which generates second image data by reducing the four sides of each pattern contained in the first image data by a predetermined width; a pattern number detector which detects a first pattern number that is the number of patterns contained in the first image data, and which also detects a second pattern number that is the number of patterns contained in the second image data; and a defect detector which detects a defect present in the patterns of the sample in accordance with a result of comparison between the first pattern number and the second pattern number.
The above objects of the present invention are also achieved by a computer-readable recording medium in which a program is recorded, the program providing a computer with functions of: a first image data generator which generates first image data from a pattern image captured from a sample; a second image data generator which generates second image data by reducing the four sides of each pattern contained in the first image data by a predetermined width; a pattern number detector which detects a first pattern number that is the number of patterns contained in the first image data, and which also detects a second pattern number that is the number of patterns contained in the second image data; and a defect detector which detects a defect present in the patterns of the sample in accordance with a result of comparison between the first pattern number and the second pattern number.
By the use of the above recording media, the pattern inspection method and apparatus of the present invention can be realized.
The above and other objects and features of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings.